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The investigation of shock wave boundary layer interaction (SWBLI) and the prediction of the associated flow field and surface property variation are essential elements in designing scramjet engine. Therefore, the present study on SWBLI is carried out numerically on a two-dimensional scramjet intake model. The effect of various free-stream and wall conditions on the surface pressure, the skin friction coefficient and performance of the intake model are analysed. It is observed that increase in the Mach number and the free-stream temperature reduces the size of the separation zones within intake. The larger separation zones are observed by increasing the wall temperature. It is noted that the behaviour of SWBLI at ramp junction and isolator inlet are dissimilar and the ratio of free-stream stagnation temperature to wall temperature does not govern the parameter for separation bubble at isolator inlet. The present investigations recommend that the Mach number has significant influence while the wall temperature and the free-stream temperature have a little effect on the performance of the intake. [ABSTRACT FROM AUTHOR]

This investigation describes the hydromagnetic flow of gravity-driven couple stress hybrid nanofluid past a heated plate. The carbon nanotubes (CNTs) are used to characterize the hybrid nanofluid. The heated plate is placed vertically with an application of homogenous-heterogeneous reactions to the assumed flow system. The homogeneous reaction governs by isothermal cubic autocatalytic kinetics while the heterogeneous reaction governs by the first order kinetics. For current study the couple stress hybrid nanofluid is presumed to be conducted electrically with impact of non-uniform magnetic effects. An appropriate set of dimensionless quantities has employed to governing equations and then has solved by homotopy analysis method. The influence of emerging parameters encountered in this work has discussed in detail with the help of graphs. In this study it has examined that, flow of fluid reduces with upsurge in magnetic parameter and volumetric concentrations, whereas thermal and concentration characteristics augment with increase in volumetric concentrations. Moreover, growth in Prandtl number leads to a reduction in thermal characteristics and growth in Schmidt number result a reduction in concentration profile. The impact of various emerging parameters has also studied numerically upon physical quantities. It has established that, with augmentation in values of buoyancy parameter there is a growth in the values of skin friction. A comparison has also carried out between current and established results with a fine agreement in both results. [ABSTRACT FROM AUTHOR]

This article presents the implementation of a numerical solution of bioconvective nanofluid flow. The boundary layer flow (BLF) towards a vertical exponentially stretching plate with combination of heat and mass transfer rate in tangent hyperbolic nanofluid containing microorganisms. We have introduced zero mass flux condition to achieve physically realistic outcomes. Analysis is conducted with magnetic field phenomenon. By using similarity variables, the partial differential equation which governs the said model was converted into a nonlinear ordinary differential equation, and numerical results are achieved by applying the shooting technique. The paper describes and addresses all numerical outcomes, such as for the Skin friction coefficients (SFC), local density of motile microorganisams (LDMM) and the local number Nusselt (LNN). Furthermore, the effects of the buoyancy force number, bioconvection Lewis parameter, bioconvection Rayleigh number, bioconvection Pecelt parameter, thermophoresis and Brownian motion are discussed. The outcomes of the study ensure that the stretched surface has a unique solution: as Nr (Lb) and Rb (Pe) increase, the drag force (mass transfer rate) increases respectively. Furthermore, for least values of Nb and all the values of Nt under consideration the rate of heat transfer upsurges. The data of SFC, LNN, and LDMM have been tested utilizing various statistical models, and it is noted that data sets for SFC and LDMM fit the Weibull model for different values of Nr and Lb respectively. On the other hand, Frechet distribution fits well for LNN data set for various values of Nt. [ABSTRACT FROM AUTHOR]

Impacts of heat source/sink and radiation on fluid flow and heat transfer past a permeable exponentially stretching/shrinking Riga plate were studied in this work. The governing partial differential equations were reduced to higher-order nonlinear ordinary differential equations using a suitable similarity transformation. The reduced equations are then numerically solved using the MATLAB software boundary value problem solver. The behavior of the skin friction coefficient and heat transfer is visually represented using numerical results. According to the findings, the modified Hartmann number significantly affects the heat transfer rate and the skin friction coefficient. The results also showed that the modified Hartmann number could be used as a controller for the heat transfer rate in case of radiation and heat source/sink occurrence. [ABSTRACT FROM AUTHOR]

A three-dimensional model of viscous magnetohydrodynamic Newtonian fluid flow bounded by an exponentially stretching plate is developed. The fluid velocity, temperature and concentration are assumed to be distributed exponentially. With the help of non-similarity transformation, the partial differential governing equations are converted to ordinary differential equations and then the problem is solved using the bvp4c MATLAB program. The collective results are compared with those of earlier studies in a limiting case and found to be in good agreement. The numerical results on the Newtonian fluid flow (velocity profile and skin friction coefficient), the changes of the fluid temperature (temperature profile and local Nusselt number), and the differences of fluid mass (concentration profile and local Sherwood number) are presented graphically. The fluid velocity and the skin friction coefficient increase with the increment of the mixed convection parameter and decrease with the increment of the magnetic field parameter. On the other hand, the heat (local Nusselt number) and mass (local Sherwood number) transfer increases with the increment of the stretching parameter. [ABSTRACT FROM AUTHOR]

This study addresses numerical solutions of a magnetohydrodynamic Casson fluid considering the temperature and concentration gradients. First, two-dimensional partial differential governing equations (PDEs) are considered to develop a mathematical model. Next, similarity variables are applied to modify the PDEs into ordinary differential equations (ODEs). The converted equations are numerically solved with the help of the bvp4c Matlab program. Impacts of the magnetic field and shrinking parameter on the skin friction, Nusselt number and Sherwood number along with the profiles of velocity, temperature, and concentration are displayed through graphs. Finally, the obtained results are validated by comparing with previously published ones. Furthermore, stability analysis is made due to dual numerical solutions to select the stable one, and the first solution is considered stable. [ABSTRACT FROM AUTHOR]

Pipe flow has been a challenge that gave rise to investigations on turbulence—long before turbulence was discerned as a research problem in its own right. The discharge of water from elevated reservoirs through long conduits such as for the fountains at Versailles suggested investigations about the resistance in relation to the different diameters and lengths of the pipes as well as the speed of flow. Despite numerous measurements of hydraulic engineers, the data could not be reproduced by a commonly accepted formula, not to mention a theoretical derivation. The resistance of air flow in long pipes for the supply of blast furnaces or mine air appeared even more inaccessible to rational elaboration. In the nineteenth century, it became gradually clear that there were two modes of pipe flow, laminar and turbulent. While the former could be accommodated under the roof of hydrodynamic theory, the latter proved elusive. When the wealth of turbulent pipe flow data in smooth tubes was displayed as a function of the Reynolds number, the empirically observed friction factor served as a guide for the search of a fundamental law about turbulent skin friction. By 1930, a logarithmic "wall law" seemed to resolve this quest. Yet pipe flow has not been exhausted as a research subject. It still ranks high on the agenda of turbulence research—both the transition from laminar to turbulent flow and fully developed turbulence at very large Reynolds numbers. [ABSTRACT FROM AUTHOR]

The role of nanofluids is of fundamental significance in the cooling process of small electronic devices including microchips and other associated gadgets in microfluidics. With such astounding applications of nanofluids in mind, it is intended to examine the flow of magnetohydrodynamic nanofluid comprising a novel combination of multi-walled carbon nanotubes and engine oil over a stretched rotating disk. The concentration equation is modified by considering the autocatalytic chemical reaction. The succor of the bvp4c numerical technique amalgamated with the response surface methodology is secured for the solution of a highly nonlinear system of equations. The sensitivity analysis is performed using a response surface methodology. The significant impacts of the prominent arising parameters versus involved fields are investigated through graphical illustrations. It is observed that the skin friction coefficient and local Nusselt number are positively sensitive to nanoparticle volume fraction while it is positively sensitive to the suction parameter. It is negatively sensitive to the Magnetic parameter. The skin friction coefficient is negatively sensitive to all input parameters. [ABSTRACT FROM AUTHOR]

The present study experimentally determines the transitional Reynolds number range for plane channel flow and characterizes its transitional state. The pressure along the channel is measured to determine the skin friction coefficient as function of Reynolds number from the laminar state, through the transitional region into the fully turbulent state. The flow structure was studied through flow visualisation which shows that as the Reynolds number increases from the laminar state the transitional region starts showing randomly occurring turbulent spots. With increasing Reynolds number the spots shift into oblique patches and bands of small scale turbulence that form across the channel width, together with large-scale streaky structures found in areas between the turbulent regions. An image analysing technique was used to determine the intermittency factor, i.e. the turbulence fraction in the flow, as function of Reynolds number. It is found that the skin friction coefficient reaches its turbulent value before the flow is fully turbulent (the intermittency factor is still below one). This suggests that the observed streaky structures in non-turbulent regions contribute to the enhancement of the wall-normal transfer of momentum. Also above the Reynolds numbers where the turbulent skin friction coefficient has been established large-scale features consisting of irregular streaky structures are found. They have an oblique shape similar to the non-turbulent and turbulent patches in the transitional flow indicating that the transition process is not fully complete even above the Reynolds number where the skin friction reaches its turbulent level. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated thermally stratified MHD flow of an Oldroyd-B fluid over an inclined stretching surface in the presence of heat generation/absorption. Similarity solutions for the transformed governing equations are obtained. The reduced equations are solved numerically using the Runge–Kutta Fehlberg method with shooting technique. The influences of various involved parameters on velocity profiles, temperature profiles, local skin friction, and local Nusselt number are discussed. Numerical values of local skin friction and local Nusselt number are computed. The significant outcomes of the study are that the velocity decreases when the radiation parameter R d is increased while the temperature profile is increased for higher values of radiation parameter R d in case of opposing flow, moreover, growth in Deborah number β 2 enhance the velocity and momentum boundary layer. The heat transfer rate is decrease due to magnetic strength but increase with the increased values of Prandtl and Deborah numbers. The results of this model are closely matched with the outputs available in the literature. [ABSTRACT FROM AUTHOR]

The main features of present numerical model is to explore and compare the behavior of simple and hybrid nanoparticles, which were allowed to move on a spreading sheet. The effect of magnetic dipole on hybrid nanofluid flow is considered. A magnetic dipole combined with hybrid nanofluid plays a vital role in controlling the momentum and thermal boundary layers. In view of the impacts of a magnetic dipole on the simple and hybrid nanofluids, steady, laminar and boundary layer flow of C u / H 2 O and C u − A l 2 O 3 / H 2 O are characterized in this analysis. The governing equations of flow problem are diminished to ordinary differential equation (ODE's) by using similarity approach. For the numerical solution of the nonlinear ODE's, Runge Kutta order 4th technique has been executed. The impact of various physical constraints, such as volume friction, viscous dissipation, Prandtl number and so on have been sketched and briefly discussed for velocity and temperature profile. In this work, some vital characteristics such as skin friction, Curie temperature and local Nusselt number are chosen for physical and numerical analysis. It has been noted that the hybrid nanofluid is more efficient in thermal conduction due to its strong thermal characteristics as compared to simple nanofluid. From results, it is also observed that the turbulence of fluid flow can be controlled through magnetic dipole. [ABSTRACT FROM AUTHOR]

The shape of the needle tip that is currently used in the medical field is a "lancet point," which is a diagonally cut cylindrical pipe, further cut on both sides. The shape of the needle shank is typically cylindrical. In this paper, tip and shank shapes that differ from the standard shape are experimentally investigated for the purpose of reducing puncture resistance. Microneedles of various cross-sectional shapes, such as polygonal and star-like, were fabricated using stereo laser lithography. Before the needle penetrates the skin, sharp edges at the needle tip may be effective to generate a stress concentration on the skin, inducing a skin fracture. After the needle penetrates the skin, corners in the cross section of the needle shank may effectively reduce the frictional resistance because the contact area between the skin and needle is limited at the corners. A needle insertion experiment was conducted against an artificial skin made of polydimethylsiloxane. The puncture resistance decreased respectively for the circular needle, polygonal needle, and star-shaped needle. For the star-shaped needles, the maximum resistance decreased as the number of corners (N) decreased. For the polygonal needle, the maximum resistance increased as N increased from 3 to 5; however, there was no observable difference for N from 6 to 8. The experimental results show that a triangular star-shaped microneedle is the most effective in reducing the puncture resistance. [ABSTRACT FROM AUTHOR]

The time-dependent barrier passage of two-dimensional non-Ohmic damping system is studied in the framework of statistical Langevin reactive dynamics. The stationary transmission coefficient is found to be a nonmonotonic function of the exponent δ which reveals an intrinsic effect of the friction’s non-Markovian character on the two-dimensional reactive process; the coupling between nonreactive and reactive modes results in an optimal path for the reactant in all cases of non-Ohmic friction. A big net flux resulted from the less barrier recrossing behavior in the two-dimensional non-Ohmic friction case. [ABSTRACT FROM AUTHOR]

Abstract Boundary layer solutions are introduced in order to provide a numerical treatment of nonlinear steady natural convection flow of non-Newtonian micropolar fluid due to an isothermal vertical permeable cone with the impact of homogeneous-heterogeneous reactions. The resulting transformed boundary layer flow equations are solved numerically by the aid of implicit finite difference technique. Additionally, the fluctuations of skin friction, couple stress coefficients and Nusselt number for various interesting sundry parameters are depicted graphically and discussed. From the obtained results, the coefficient of couple stress increases for larger values of surface temperature exponent n whereas reverse trend is clarified through vortex viscosity parameter K. Once again, it is found from current contribution that concentration of the micropolar fluid is decreases function by increasing the strength of homogeneous and heterogeneous reactions. The code of numerical technique is validated by comparing our data with previous published contributions and a good agreement is given. [ABSTRACT FROM AUTHOR]

The present study focuses on the non-Newtonian magnetohydrodynamic flow, under the kinetic postulate, of fluids that are initially liquid past a porous plate in the appearance of thermal radiation effects. Resemblance transfigurations are used to metamorphose the governing equations for temperature and velocity into a system of ordinary differential equations. We then solved these differential equations subject to convenient boundary conditions by using the shooting method along with the Runge–Kutta method. Heat transfer and characteristic flow results are acquired for different compositions of physical parameters. These results are extended graphically to demonstrate interesting attributes of the physics of the problem. Nusselt number and skin friction coefficients are also discussed via graphs and tables for different values of dimensionless parameters. Decline occurs in velocity profile due to escalating values of M. Temperature profile depicts growing behavior due to acceleration in the values of λ and M. Nusselt number and skin friction curves represent rising behavior according to their parameters. [ABSTRACT FROM AUTHOR]

Highlights • This study presents experimental studies of the single-phase resistance. • Study of resistance characteristics in rod bundles under low Reynolds number. • An improved correlation of the frictional resistance coefficient is obtained. • Introduce kinematic viscosity correction factor for correction. • This newly developed correlation predicts data with a relative error within ±5%. Abstract A considerable amount of research has gone into understanding the thermal-hydraulics characteristics of rod bundle channels which is of great importance for the nuclear industry. This paper will show that the development of the correlation of the frictional resistance coefficient in rod bundle channels under natural circulation conditions is well understood. This paper presents experimental studies of the single-phase resistance and obtains an improved correlation of the frictional resistance coefficient under natural circulation conditions based upon thermal-hydraulics characteristics which are well understood. It is also shown that this newly developed correlation closely predicts data. The experimental results show that the frictional resistance coefficient of a rod bundle channel under natural circulation is related to the physical properties of fluid and the size of the rod bundle channel. According to different flow regions, the relationship between the frictional resistance coefficient and Reynolds number is discussed separately, and the expressions of frictional resistance coefficient with Reynolds number in laminar flow region and transition region are obtained. After considering the influence of fluid properties on the frictional resistance coefficient, this paper introduces the kinematic viscosity correction factor to correct the frictional resistance coefficient. Finally, the complete expression of the frictional resistance coefficient was obtained. This newly developed predictive expression is in good agreement with experimental data in both the laminar and transition flow regions, with a relative error within ±5%. Thus we now have a predictor of the frictional resistance coefficient under natural circulation conditions based upon more complete thermal-hydraulic parameters in a static state. [ABSTRACT FROM AUTHOR]

Graphical abstract The physical model is intended to portray the schematic of the problem and behaviour of skin friction and Nusselt number. Highlights • The review describe the physical properties of Carreau nanofluids. • Flow past a wedge shaped geometry is studied. • Heat and mass transfer characteristics are further analyzed. • Effect of thermal radiation on heat transfer rate are investigated. • Numerical solutions are computed via collocated numerical method. Abstract In this article, an innovative revised Buongiorno's model is employed to investigate the flow of Carreau nanofluids generated by a wedge-shaped geometry. Moreover, heat and mass transfer characteristics are explored under the influence of non-linear thermal radiation. At first, the developed flow equations are made dimensionless via suitable transformations and then resulting set of nonlinear ordinary differential equations are solved numerically using built-in MATLAB solver bvp4c. It is observed that the solution of current flow problem is highly dependent on the contribution of several physical parameters like Weissenberg number, power-law index, wedge angle parameter, velocity ratio parameter, non-linear radiation parameter, suction parameter, Brownian motion and thermophoresis parameters, Lewis and Prandtl numbers. Detailed analysis for the novel results of dimensionless velocity, temperature and nanoparticles concentration with in the boundary layer region is exhibited graphically. The core physical implication of the computed results is that the thermal boundary layer is thinned by higher radiation parameter. This study reveals that an enhancement in the local Nusselt number is noted with higher temperature ratio parameter. On the other hand, an incremental skin friction ate the wall can be achieved by growing values of power-law index. The obtained data is distinguished with earlier studies and admirable agreement has been noted. [ABSTRACT FROM AUTHOR]

As the Reynolds number increases, the skin friction has been identified as the dominant drag in many practical applications. In the present paper, the effects of the Reynolds number on the mean skin friction decomposition in turbulent channel flows up to Reτ= 5 200 are investigated based on two different methods, i.e., the Fukagata-Iwamoto-Kasagi (FIK) identity (FUKAGATA, K., IWAMOTO, K., and KASAGI, N. Contribution of Reynolds stress distribution to the skin friction in wall-bounded flows. Physics of Fluids, 14(11), L73-L76 (2002)) and the Renard-Deck (RD) identity (DECK, S., RENARD, N., LARAUFIE, R., and WEISS, P. É. Large-scale contribution to mean wall shear stress in high-Reynolds-number flat-plate boundary layers up to Reθ= 13 650. Journal of Fluid Mechanics, 743, 202-248 (2014)). The direct numerical simulation (DNS) data provided by Lee and Moser (LEE, M. and MOSER, R. D. Direct numerical simulation of turbulent channel flow up to Reτ≈ 5 200. Journal of Fluid Mechanics, 774, 395-415 (2015)) are used. For these two skin friction decomposition methods, their decomposed constituents are discussed and compared for different Reynolds numbers. The integrands of the decomposed constituents are locally analyzed across the boundary layer to assess the actions associated with the inhomogeneity and multi-scale nature of turbulent motion. The scaling of the decomposed constituents and their integrands are presented. In addition, the boundary layer is divided into three sub-regions to evaluate the contributive proportion of each sub-region with an increase in the Reynolds number. [ABSTRACT FROM AUTHOR]

The paper presents the results of tilt tests using a large number of three-core samples, aiming to establish a method for determining the basic friction angle of planar rock discontinuities. The three-core tilt test is easy to operate, and the results are comparable with the saw-cut method after modification. Saw-cut and two-core samples were also tested for the purpose of comparison. The test results show that the cylindrical surface of the core is slightly rougher than the surface of saw-cut samples so that the friction angle measured on the cylindrical surface of the core is slightly larger than that measured on saw-cut samples. The basic friction angle of the planar rock discontinuity is obtained by decreasing 2° from the friction angle measured on three-core samples. The appropriate number for test repetitions is 10∼20 in order to obtain a reliable mean friction angle. Grinding or polishing of the cylindrical surface of cores is not recommended, since it will lead to an increase in the friction angle in most of rock types. [ABSTRACT FROM AUTHOR]

Abstract In this paper we present a practical guideline on how to estimate the frictional resistance of ship hulls due to different fouling control coatings. Most of the current methods rely on empirical formulations based on an equivalent sand grain roughness height. These correlations are not universal and cannot be applied to every marine surface. Conversely, the shear stress of a specific coating can be measured in an experimental facility at the same Reynolds roughness number as at full scale. The results can be used to inform the boundary conditions of computational fluid dynamics, where the complex flow around the ship can be computed for any sailing condition. Hence, this methodology allows the estimation of the frictional resistance due to a specific surface in a specific sailing condition. Representative antifouling coating products by AkzoNobel, and wall functions for the open-source code OpenFOAM, are used to illustrate the methodology. Similarities and differences with other methods are discussed. Highlights • Novel methodology for full-scale friction resistance assessment. • Step by step practical guideline. • Case study demonstrating the proposed methodology. • Comparison between different methodologies. [ABSTRACT FROM AUTHOR]

The dissipation function in turbulent plane Poiseuille flows (PPFs) and plane Couette flows (PCFs) subject to spanwise rotations is analyzed. It is found that, in the PCFs without system rotations, the mean part is constant while the fluctuation part follows a logarithmic law, resulting in a similar logarithmic skin friction law as PPFs. However, if the flow system rotates in the spanwise direction, no obvious dependence on the rotation number can be evaluated. In the PPFs with rotations, the dissipation function shows an increase with the rotation number, while in the PCFs with rotations, when the rotation number increases, the dissipation function first decreases and then increases. [ABSTRACT FROM AUTHOR]

Highlights • Boiling flow phases are identified to obtain stable two-phase flow. • The flow rate decreases when the two-phase frictional resistance is large enough. • Existing models are roughly unsuitable for the natural circulation in rod bundle. • A new correlation for two-phase frictional pressure drop in rod bundle is fitted. Abstract Natural circulation boiling flow resistance characteristics in a 3 × 3 rod bundle channel are experimentally studied in this paper. In order to achieve a stable two-phase natural circulation flow, the boiling flow phases are identified and measures such as decreasing the inlet fluid subcooling degree and increasing the inlet local resistance are adopted. The ONB during the experiment is determined by the wall temperature drop. The variation of pressure drop components, including the gravity pressure drop, the frictional pressure drop and the acceleration pressure drop, is given. For high mass quality conditions, the mass flow rate is observed declining with the increasing heat flux when the frictional pressure drop and the acceleration pressure drop grow faster than the gravity pressure drop reduction. A few homogeneous flow models and separated flow models for the two-phase frictional pressure drop are compared against experimental results. The homogeneous flow models can well predict the frictional pressure drops for low mass quality conditions and the Duckler model predictions are the most accurate with a mean relative error of 15.7%. In terms of the separated flow models, the Mishima and Sun models predictions are in good agreement with experimental results respectively for low and high mass quality conditions. Based on the Chisholm correlation, a new correlation is fitted by experimental results. The friction factors obtained in single-phase experiments are used to calculate the liquid phase frictional pressure drops. The comparison against experimental results and data from other literatures shows the new correlation can well predict the two-phase frictional pressure drops under given flow conditions. [ABSTRACT FROM AUTHOR]

Abstract The frictional resistance and hole quality when drilling CFRP laminates are associated with tribological behaviors of drill materials. In the present study, tribological tests are conducted on various diamond coated WC-Co balls sliding against T800/X850 CFRP laminates with [-45/90/45/0]s lay-up, under specific conditions similar to the drilling process. It is firstly found that the coefficient of friction (COF) varies with the sliding direction. The boron-doped micro-crystalline and nano-crystalline composite diamond (BDMC-NCCD) film synthesized by optimized growth durations (9 h for BDMCD and 2.5 h for NCD) presents relatively low COF and wear rate (0.193 and 0.97 × 10−8 mm3/N m, when the sliding velocity and normal load are respectively 1.5 m/s and 5.0 N), as well as high critical load for the film peeling (35 N), owing to the nano-sized diamond grains and low surface roughness (R a ~125.09 nm measured by the confocal microscopy) of the surface NCD layer, and high hardness and favorable adhesion of the underlying BDMCD layer. Besides, influences of the sliding velocity and normal load are clarified, indicating that the COF increases with the load, but decreases with increasing the velocity, while the wear rate increases with either the load or velocity. Highlights • Tribological test condition is defined according to drilling test. • Five typical types of diamond films are tested sliding against CFRP sections. • Coefficient of friction is dependent on sliding direction. • BDMC-NCCD film synthesized by optimized durations perform the best. • Optimized growth durations are 9 h for BDMCD and 2.5 h for NCD. [ABSTRACT FROM AUTHOR]

Abstract In this paper, Energy absorption characteristics of tapered multi-cell tubes improved by foams are studied. For the energy absorption process, a theoretical formulation is developed to represent the mean crush load of the foam-filled tubes considering a combination of mean crush loads due to non-filled tube, the foam-filler, and a frictional resistance between them (interaction effects). The formulation is based on the assumptions including equivalent segmented non-tapered single-cell tubes as well as a parallel resisting force of the contributors (non-filled tubes, foam-filler, and interaction effects). Moreover, an extensive numerical analysis on the crushing of the foam-filled tapered multi-cell tubes, with a taper angle ranging from 0 to 7 degrees, a wall thickness ranging from 0.25 to 3 mm, and a cell number ranging from 11 to 10 × 10, is conducted to evaluate the effects of side wall tapering, cross section's division into multiple cells and wall thickness enlargement on the crashworthiness characteristics. Analyses indicate that there are significant enhancements in the energy absorption behavior of the foam-filled tubes with respect to the non-filled ones. As a special case, the force-displacement results obtained in the numerical simulation are verified against those experimentally observed and reported in the literature for a foam-filled non-tapered single-cell tube. [ABSTRACT FROM AUTHOR]

Purpose Pipeline maintenance technology using smart isolation tool is becoming more widely used in the global scope. This paper aims to investigate the effects of parameters on the frictional resistance between the slip and pipeline and the frictional characteristics under different lubrication films.Design/methodology/approach An experimental platform consisting of slip, pipeline and data acquisition system was developed, wherein the slip slips on the pipeline under different normal forces and velocities. In addition, three lubrication conditions, namely, dry wall, oil liquid and black powder on the wall, were investigated to study the effects of lubrications on the frictional coefficient and characteristics.Findings Research results indicate that the frictional force and coefficient were sensitive to normal force. The crude oil affected the frictional coefficient within a certain range of normal force, and the black powder enhanced the surface roughness in the natural gas pipeline. However, velocity had no effect on them. In addition, different contact behaviors could be observed from the frictional coefficient curves.Originality/value In this paper, the effects of normal force and velocity on frictional resistance of sliding slip during decelerating process in pipeline were investigated, and the effects of lubrication films on frictional characteristics were also revealed. The research results are of great value to improve the prediction accuracy of smart isolation tool, and also provide a guiding significance for the development of maintenance operation in pipelines. [ABSTRACT FROM AUTHOR]

Highlights • Flow topology was built on the boattail surfaces. • Three distinctive flow regimes were observed. • The separation bubble develops in size with growth of the angles. • The length of separation bubble increases linearly with the angles. Abstract The surface flow pattern over a conical boattail on an axisymmetric body was investigated experimentally under low-speed and turbulent-boundary-layer conditions. Seven conical boattails with the same length but different angles from 10° to 22° were tested at a Reynolds number around 4.3 × 104, based on the model diameter. The study used the global luminescent oil-film (GLOF) skin friction measurement technique. The skin friction fields were measured and the corresponding flow topologies were extracted from the GLOF measurements. The effect of oil-film thickness on the separation position was also evaluated. Experimental results showed three different flow types on the boattail surface: (1) flow without separation, (2) flow with a separation bubble, and (3) fully separated flow. The critical angles for the transitions are discussed and compared with classic results for similar boattail models. The separation bubble generated at moderate boattail angles was observed for what we believe to be the first time under low-speed conditions, and the flow topology was clearly shown by the GLOF results. The azimuthally-averaged skin friction projected on the centerline showed different trends inside and behind the reattachment position when the boattail angle increased. [ABSTRACT FROM AUTHOR]

The dynamics of large-scale coherent structures (LSCS) are investigated in a rough-bed flow over the whole water column and longitudinal and transverse turbulent fluxes of momentum are compared. The relation between LSCS and fluctuations of skin friction and near-bed surface pressure is examined in order to understand the effects of LSCS on the bed. The study was carried out in an open channel with a non-moving permeable bed of screeded loose-mixed gravel (D50 = 1.5 cm) at Reynolds numbers ranging from 3.19 × 104 to 1.08 × 105. Quasi-instantaneous full-depth three-dimensional (3D) velocity profiles with high spatial and temporal resolution measured with an acoustic Doppler velocity profiler (ADVP) are combined with the signals of a hot-film sensor mounted on the top of the gravel and a piezoresistive pressure transducer placed in the top layer of the bed particles at the centre of the channel. Vertical turbulent momentum flux is clearly dominated by ejections and sweeps over most of the water column. Near the bed, contributions of sweeps are larger than those of ejections. This is reversed at the mid-depth (z/h = 0.5). No preferential quadrant orientation is seen for the transverse momentum flux. A correlation between LSCS dynamics in the water column and data from the sensors on the bed is made evident. Sweeps correlate with positive fluctuations of bottom pressure and skin friction while ejections correlate with negative ones. [ABSTRACT FROM AUTHOR]

A systematic study has been performed on MHD convective chemically reactive and absorbing fluid along an exponentially accelerated vertical plate with the impact of Hall current by considering ramped temperature. Laplace transform technique is applied to obtain exact solutions of the non-dimensional governing equations for fluid velocity, temperature and concentration. Based on the above solutions, the expressions for skin friction coefficient, Nusselt number and Sherwood number are derived. The consequences of diverse physical parameters on flow quantities are examined thoroughly with graphical representations. The numerical values for skin friction coefficient, rate of heat transfer and rate of mass transfer are recorded and analyzed. [ABSTRACT FROM AUTHOR]

Abstract For multispan suspension bridges, the frictional resistance between main cable and saddle is vital to counterpoise unbalanced cable tension between adjacent main spans. The calculation for frictional resistance is essential for the bridge design. In this study, a numerical method for frictional resistance between main cable and saddle is developed. The proposed method is validated against large-scale saddle model tests, and then used to analyze the frictional resistance in a multispan suspension bridge. The method is used to investigate the main components of total frictional resistance, the effects of vertical friction plates, and the frictional resistance distribution along the longitudinal direction of saddle. The results indicate that the frictional resistance at the bottom and side surfaces between main cable and saddle are the main components of total frictional resistance. The distribution of frictional resistance along the longitudinal direction of saddle increases from one end to the other end of saddle. To add vertical friction plates is an effective way to increase the frictional resistance. The proposed numerical method provides an effective and feasible tool for evaluating the frictional resistance. Highlights • A numerical method is developed to evaluate the cable-saddle frictional resistance. • Main components of total cable-saddle frictional resistance are quantified. • Distribution of cable-saddle frictional resistance along the longitudinal direction of saddle is investigated. • Contribution of vertical friction plate on cable-saddle frictional resistance is explored. [ABSTRACT FROM AUTHOR]

The influence of distributed cylinder roughness elements on boundary layer transition for NACA0012 airfoil at Ma = 0.6 has been investigated by subsonic/transonic/supersonic wind tunnel experiment with oil-film interferometry. Three different heights and two different distances of cylinder roughness elements on the airfoil model were used, and the skin friction coefficient was measured by the oil-film interferometry. The experimental results show that higher roughness elements promote the transition earlier. In addition, narrower distance of roughness elements can delay the transition compared with the case of wider distance. [ABSTRACT FROM AUTHOR]

Abstract An elevated raft technique is proposed for cast-in-place bored piles, where loose sediments and excavation debris at the pile tip can be compressed by the applied load from the superstructure. The axial load-settlement (i.e., P - S curve) behaviour of bored piles with debris is evaluated by a series of model-scale laboratory experiments. Numerical simulation is conducted using a two-dimensional axisymmetric model for comparison. An analytical model is then proposed to capture the whole P - S curve in three segments: (a) the contribution of skin friction, (b) increased settlement associated with the compression of debris, and (c) the development of tip resistance. [ABSTRACT FROM AUTHOR]

This paper addresses nonlinear mixed convection flow due to Riga plate with double stratification. Heat transfer analysis is reported for heat generation/absorption and nonlinear thermal radiation. Physical problem is mathematically modeled and nonlinear system of partial differential equations is achieved. Transformations are then utilized to obtain nonlinear system of ordinary differential equations. Homotopic technique is utilized for the solution procedure. Graphical descriptions for velocity, temperature, and concentration distributions are captured and argued for several set of physical variables. Features of skin friction and Nusselt and Sherwood numbers are also illustrated. Our computed results indicate that the attributes of radiation and temperature ratio variables enhance the temperature distribution. Moreover, the influence of buoyancy ratio and modified Hartmann number has revers effects on rate of heat transfer. [ABSTRACT FROM AUTHOR]

Thermobioconvection boundary layer flow in a suspension of water-based bionanofluid holding both nanoparticles and motile microorganisms past a wedge surface was studied. The governing nonlinear partial differential equations on reference of the Buongiorno model were transformed into a set of coupled nonlinear ordinary differential equations. Shooting technique was then used to solve the transformed nonlinear ordinary differential equations numerically. The solutions were found to be contingent on several values of the governing parameters. As highlighted, the velocity profile as well as the skin friction coefficient was affected by the pressure gradient parameter, the function of the wedge angle parameter. On the other hand, the temperature, nanoparticle concentration, and density of motile microorganism’s distributions together with its corresponding local Nusselt number, local Sherwood number, and local density of the motile microorganisms change with the thermophoresis and Brownian motion parameter and so Lewis number, Schmidt number, and bioconvection Péclet number. An experimental scheme together with sensitivity analysis on the basis of Response Surface Methodology (RSM) was applied to examine the dependency of the response parameters of interest to the input parameters’ change. Obviously, local Nusselt number was more sensitive towards the Brownian motion parameter when the Brownian motion parameter was at 0.2 and 0.3. However local Sherwood number was more sensitive towards the Lewis number for all values of Brownian motion parameter. Compatibility found by comparing results between RSM and shooting technique gave confidence for the model’s accuracy. The findings would provide initial guidelines for future device fabrication. Finally, the numerical results obtained were thoroughly inspected and verified with the existing values reported by some researchers. [ABSTRACT FROM AUTHOR]

Water hammer and column separation induced by simultaneous and sequential (delayed) closure of two valves may occur in industrial pipeline systems. This paper deals with such cases both experimentally and numerically. Water hammer equations are solved by the method of characteristics. Transient cavitating pipe flow is simulated by a discrete gas cavity model (DGCM) that considers unsteady skin friction. Discrete gas cavities and Zielke's convolution-based unsteady skin friction term are explicitly incorporated in the staggered grid algorithm of the method of characteristics. Experiments have been performed in a laboratory pipeline apparatus. The apparatus consists of an upstream end tank, a horizontal steel pipeline (total length 55.37 m, inner diameter 18 mm), four valve units positioned along the pipeline including the end points, and a downstream end tank. A transient event is induced either by simultaneous or sequential closure of two end valves. Numerical results are compared and verified with results of measurements. In addition, a theoretical analysis of pressure wave fronts travelling along the pipeline is also presented to clearly show profound effects of wave interactions. [ABSTRACT FROM AUTHOR]

Analysis of the mechanism of frictional interaction of parts in sealing units of industrial equipment showed the importance of evaluation of the factors affecting the friction coefficient and leak-tightness while designing these parts. [ABSTRACT FROM AUTHOR]

In view of the characteristics of low permeability and tight reservoir and the requirement of fracturing fluid, the fracturing fluid system of ma-s high efficiency drag reducer is developed, and its performance is evaluated. Using the indoor evaluation device of drag reducer, the Ma-s high efficiency drag-reducing agent fracturing fluid system has high drag reduction performance, the best concentration is 0.07%, and has a certain stability, the 120h drag reduction rate is lowered by 8%. The resistance to mild and shear properties was tested by Rheometer, the temperature rises from 25 to OC, viscosity drops 0. 025pa.s, shearing time from 0 s to 1800s, apparent viscosity reduces 0.0075 Pa.s, when the velocity is 20m/s, the drag reduction rate is 61%, then with the flow rate increases, the drag reduction rate drops, But the decline was smaller, at a minimum of 53%. With the successful application of 5 wells in the field of ma-s drag-reducing agent fracturing fluid, the maximum frictional resistance of the tubing can be reduced by 61%, which provides an effective way for the efficient reconstruction of tight reservoirs. [ABSTRACT FROM AUTHOR]

Periodic wall oscillations in the spanwise or circumferential direction can greatly reduce the friction drag in turbulent channel and pipe flows. In a concentric annulus, the constant rotation of the inner cylinder can intensify turbulence fluctuations and enhance skin friction due to centrifugal instabilities. In the present study, the effects of the periodic oscillation of the inner wall on turbulent flows through concentric annulus are investigated by the direct numerical simulation (DNS). The radius ratio of the inner to the outer cylinders is 0.1, and the Reynolds number is 2 225 based on the bulk mean velocity Um and the half annulus gap H. The influence of oscillation period is considered. It is found that for short-period oscillations, the Stokes layer formed by the circumferential wall movement can effectively inhibit the near-wall coherent motions and lead to skin friction reduction, while for long-period oscillations, the centrifugal instability has enough time to develop and generate new vortices, resulting in the enhancement of turbulence intensity and skin friction. [ABSTRACT FROM AUTHOR]

The super-long and large-diameter steel pipe piles are often adopted for the construction of offshore oil platforms in deep sea. One constructability issue related to driving heavy pipe piles is the pile running. The term pile running refers to the quick penetration of a pile into the seabed as a result of its high self-weight and low resistance from the seabed. The unexpected pile running can cause the steel wire of the hammer to break or even the loss of the hammer. A case study of pile running at an oil platform is introduced in this paper. A simplified theoretical method is proposed to explain the mechanisms of the pile running in this case. A factor of friction degradation is proposed to calculate the dynamic skin friction from the static ultimate skin friction of surrounding soil. The comparisons between the predictions to the case history show that the proposed simplified method can be used to predict the pile running condition. [ABSTRACT FROM AUTHOR]

The failure mode of a free corner in masonry buildings, still poorly investigated, is one of the most common failure mechanisms occurring and clearly recognizable in the aftermath of a seismic event. It is characterized by the formation of a masonry wedge, mainly due to the thrust of roof elements in addition to inertial forces, and it generally involves rocking-sliding motions along the cracks on the interlocked orthogonal walls. The onset of this failure mode is herein analyzed by means of an upgraded macro-block model, based on the kinematic approach of limit analysis and accounting for the influence of frictional resistances on the collapse load multiplier and the related crack pattern. An original criterion weighting the role of rocking vs. sliding motion on the collapse load factor is developed and a formulation with general applicability is obtained. Several parametric analyses are performed in order to highlight the influence of geometrical, mechanical and loading parameters on the seismic capacity of the corner. The reliability of the proposed model and solution procedure is confirmed through the comparison with the results provided by other macro-block models existing in the literature. The final perspective is the next implementation of the proposed model in FaMIVE (Failure Mechanism Identification and Vulnerability Evaluation) applicative. [ABSTRACT FROM AUTHOR]

This article investigates the unsteady flow and heat transfer in a nanofluid over a stretching/shrinking sheet with injection/suction effects to overcome the deficiency found in the previous model that was to control the nanoparticles fraction actively. Besides, this study controls the nanoparticles volume fraction on the boundary passively rather than actively in order to make the model physically more realistic with zero flux at the surface. This approach makes the Buongiorno's nanofluid model more effective for the plate problems in reality. The governing partial differential equations are transformed into ordinary differential equations via the similarity transformation and are then solved numerically using the bvp4c function. Effects of different flow parameters on the velocity profile, the temperature distribution, the skin friction coefficient and the local Nusselt number are deliberated in detail. Dual solutions are observed for the stretching/shrinking sheet and suction/injection parameter in some certain range. Stability analysis is conceived to check the reliability and stability of the solutions. The local Nusselt number is estimated through multiple linear and quadratic regressions. A comparison is made to validate the obtained results. Results indicate that the first solution is stable and physically realizable as compared to the second solution either fluid flow is under suction or injection effect. The Brownian motion parameter is not significant, and the local Nusselt number is almost independent of the Brownian motion parameter, but it depicts decreasing behavior for the Schmidt number and the thermophoresis parameter for suction and opposite behavior for the injection case. The rise in the suction parameter causes the streamlines to get closer to each other while for the impermeable case, the oncoming flow is the same as for the stagnation point flow. [ABSTRACT FROM AUTHOR]

Bed particle entrainment by turbulent wall-shear flow is a key topic of interest in hydrodynamics because it plays a major role to govern the planetary morphodynamics. In this paper, the state-of-the-art review of the essential mechanisms governing the bed particle entrainment by turbulent wall-shear flow and their mathematical modeling is presented. The paper starts with the appraisal of the earlier multifaceted ideas in modeling the particle entrainment highlighting the rolling, sliding, and lifting modes of entrainment. Then, various modeling approaches of bed particle entrainment, such as deterministic, stochastic, and spatiotemporal approaches, are critically analyzed. The modeling criteria of particle entrainment are distinguished for hydraulically smooth, transitional, and rough flow regimes. In this context, the responses of particle size, particle exposure, and packing condition to the near-bed turbulent flow that shears the particles to entrain are discussed. From the modern experimental outcomes, the conceptual mechanism of particle entrainment from the viewpoint of near-bed turbulent coherent structures is delineated. As the latest advancement of the subject, the paper sheds light on the origin of the primitive empirical formulations of bed particle entrainment deriving the scaling laws of threshold flow velocity of bed particle motion from the perspective of the phenomenological theory of turbulence. Besides, a model framework that provides a new look on the bed particle entrainment phenomenon stemming from the stochastic-cum-spatiotemporal approach is introduced. Finally, the future scope of research is articulated with open questions. [ABSTRACT FROM AUTHOR]

In this paper, condensing pressure drop of refrigerant-based nanofluid inside a tube is studied. Isobutene was selected as the base fluid while CuO nanoparticles were utilized to prepare nano-refrigerant. However, for the feasibility of nanoparticle dispersion into the refrigerant, Polyester oil (POE) was utilized as lubricant oil and added to the pure refrigerant by 1% mass fraction. Various values of mass flux, vapor quality, concentration of nanoparticle are investigated. Results indicate that adding nanoparticles leads to enhance frictional pressure drop. Nanoparticles caused larger pressure drop penalty at relatively lower vapor qualities which may be attributed to the existing condensation flow pattern such that annular flow is less influenced by nanoparticles compared to intermittent flow regime. [ABSTRACT FROM AUTHOR]

The experiments were carried out using an Optimol SRV5 oscillating wear tester under lubrication. Specimens were cut from gray cast iron cylinder liners honed and/or plateau honed with diamond or ceramic stones. Counter-specimens were cut from chromium-coated compression ring. Short time tests of 30 min duration were conducted at a temperature of −20 °C, with a stroke of 3 mm. In addition, for a few sliding assemblies, durations of tests at the low temperature were extended to 24 h. For comparison, similar tests for a smaller number of sliding pairs were carried out at a temperature of 80 °C. Before and after tests cylinder liner surface topographies were measured by a white light interferometer Talysurf CCI Lite. It was found that the changes of liner height and frictional resistance at the low temperature were smaller from those tested at the elevated temperature. Two-process textures tested at the low temperature led to a smaller final coefficient of friction, compared to one-process surfaces; opposed results were obtained at the high temperature. [ABSTRACT FROM AUTHOR]

In the present paper presented are the results of prediction of total resistance of inland waterway vessels based on model test data. In scaling the resistance from model to full scale the extrapolation with two-dimensional frictional resistance formulation (without form factor) was applied, combined with different methods of determination of frictional (viscous) resistance coefficient. There were used the equations that include the effect of water depth, with and without account for pressure gradient. It was shown that limited depth of water substantially affects the frictional resistance. The results of example calculations are compared to resistance prediction made using the ITTC 1957 model- ship correlation line. Example calculations take into account the limited depth of water. Depending on the applied method of determination of frictional resistance coefficient the resultant total resistance of inland waterway vessel is higher or lower than the resistance based on the ITTC 1957 correlation line. The effect of water depth depends on the ratio of water depth to ship draught (h/T), on ship speed, and on the composition of a convoy. The extrapolation of resistance was made without including the form factor. Computations are made based on model test data for an inland waterway cargo vessel, for a kombi-type convoy of an inland waterway cargo vessel and a dumb barge, and for a convoy of two dumb barges without a pushboat. [ABSTRACT FROM AUTHOR]